You don't get to choose, you get all that apply. It's a single triggered ability at the beginning of combat, and the effect lasts until end of turn.
E.g.
You have: Typhoid Rats, Wind Drake and Odric, Lunarch Marshal. At the beginning of combat the ability triggers, when it resolves all your three creatures gain deathtouch and flying until end of turn.
Edit: Notified the mods about this being in the wrong forum. FYI, the right place for questions like this is the Magic Rulings subforum.
Chandra, Torch of Defiance - Oops! All Chandras.
Prime Speaker Zegana - Draw for Power.
Pir & Toothy - Counterpalooza.
Arcades, the Strategist - Another Brick in the Wall.
Zacama, Primal Calamity - Calamity of Double Mana.
Edgar Markov - Vampires Don't Die.
Child of Alara - Dreamcrusher.
Odric, Lunarch Mashal
But why post here?
E.g.
You have: Typhoid Rats, Wind Drake and Odric, Lunarch Marshal. At the beginning of combat the ability triggers, when it resolves all your three creatures gain deathtouch and flying until end of turn.
Edit: Notified the mods about this being in the wrong forum. FYI, the right place for questions like this is the Magic Rulings subforum.
Chandra, Torch of Defiance - Oops! All Chandras.
Prime Speaker Zegana - Draw for Power.
Pir & Toothy - Counterpalooza.
Arcades, the Strategist - Another Brick in the Wall.
Zacama, Primal Calamity - Calamity of Double Mana.
Edgar Markov - Vampires Don't Die.
Child of Alara - Dreamcrusher.